1. Field of the Invention
The present invention relates to an exposure method, exposure apparatus, and device manufacturing method and, more particularly, to an exposure method and apparatus used in a lithography process for manufacturing a semiconductor device, liquid crystal display device, image pick-up device (such as a CCD), thin-film magnetic head, or the like and a device manufacturing method using the exposure method and apparatus in the lithography process.
2. Description of the Related Art
Conventionally, in a lithography process for manufacturing semiconductor devices and the like, various types of exposure apparatuses designed to form predetermined patterns on a substrate such as a wafer or glass plate (to be referred to as a xe2x80x9cwaferxe2x80x9d or xe2x80x9csubstratexe2x80x9d hereinafter, as needed). Recently, with increases in the degree of integration of semiconductor devices, the following exposure apparatuses are mainly used: a step-and-repeat type reduction projection exposure apparatus (so-called stepper) capable of transferring fine patterns formed on a mask or reticle (to be generically referred to as a xe2x80x9creticlexe2x80x9d hereinafter) onto a plurality of shot areas on a wafer coated with a photoresist through a projection optical system with a relatively high throughput and high precision and a sequential moving type projection exposure apparatus such as a step-and-scan type scanning exposure apparatus (so-called scanning stepper) obtained by improving the above stepper.
The resolution of the projection optical system of such a projection exposure apparatus can be expressed by R=k1xc2x7xcex/N.A., as is well-known as the Rayleigh formula, where R is the resolution of the projection optical system, xcex is the wavelength of exposure light, N.A. is the numerical aperture of the projection optical system, and k1 is a constant determined by the resolution of a photoresist and other processes. To improve the resolution of the projection optical system, therefore, the numerical aperture N.A. may be increased.
A depth of focus DOF of the projection optical system is expressed by DOF=k2xc2x7xcex/(N.A.)2 where k2 is a proportional constant. If, therefore, the numerical aperture N.A. is simply increased, the depth of focus DOF may become too small. It is known that when periodic lattice patterns like patterns for memory circuit portions are to be exposed, the depth of focus can be substantially increased, with the resolution being improved, by a so-called modified illumination method of tilting the principal ray of exposure light from an illumination optical system.
It is also known that when isolated patterns such as contact hole patterns are to be exposed, the depth of focus of the projection optical system can be substantially (apparently) increased by a so-called FLEX method, DP exposure method, CDP exposure method, or the like in which the positional relationship between a wafer and the imaging plane of the projection optical system in the optical axis direction of the projection optical system is continuously or intermittently changed according to a desired procedure so that an irradiation area on the wafer surface which is irradiated with exposure light through the projection optical system is always located in a range having a predetermined width in the optical axis direction, which includes the imaging plane, and the distribution of light amounts supplied onto the wafer, corresponding to the relative positions of the imaging plane and wafer surface, becomes a predetermined distribution. Exposure methods of substantially increasing the depth of focus of the projection optical system by continuously or intermittently changing the positional relationship between the imaging plane and the wafer in the optical axis direction of the projection optical system according to the desired procedure will be generically referred to as a progressive focus exposure method hereinafter. For example, the progressive focus exposure method used by a static exposure apparatus such as a stepper is disclosed in, for example, Japanese Patent Laid-Open Nos. 63-42122 and 5-13305. The progressive focus exposure method used by a scanning exposure apparatus such as a scanning stepper is disclosed in, for example, Japanese Patent Laid-Open Nos. 4-277612 and 6-314646.
In the conventional progressive focus exposure method disclosed in each of the above references, when patterns such as contact hole patterns are to be transferred onto a plurality of shot areas on a wafer, exposure is performed under the same conditions (e.g., the relative moving range (so-called Z swing width) of the wafer surface with datum to an imaging plane, light amount) for each shot area.
According to the principle of resist coating by a coater (resist coating unit), the thickness of a photosensitive agent (resist) layer formed on the wafer varies from a central portion to peripheral portion of the wafer. In addition, the thickness distribution of the resist layer on the wafer is unique to each resist coating unit. Conventionally, such variations in resist layer thickness have hardly raised problems. With further increases in the degree of integration of semiconductor devices, accompanied with a reduction in circuit pattern size, and an increase in wafer size, variations in the shapes of isolated pattern images, mainly contact hole pattern images, among shot areas due to variations in resist layer thickness cannot be neglected.
Semiconductor devices will further increase in the degree of integration in the future, and wafers tend to further increase in size. It is therefore expected that variations in the shapes of isolated pattern images such as contact hole pattern images due to the above variations in resist layer thickness will further become noticeable.
In a liquid crystal exposure apparatus or the like, patterns having different shapes are transferred onto a plurality of shot areas on the same substrate with relatively high frequency. Such operation is sometimes performed in a semiconductor exposure apparatus. In such a case, patterns having different shapes are formed in shot areas on the respective layers on the substrate. For this reason, when overlay exposure is performed on a subsequent layer, detection light from a focus sensor for detecting the position (focus position) of the substrate in the optical axis direction of the projection optical system may be affected by stepped portions on the surface due to the shapes of patterns that have already been formed on the substrate or the difference in thickness between resist layers, resulting in a detection error. As in the above case, a plurality of patterns transferred onto the respective shot areas may not be formed in desired shapes with high precision owing to variations in resist layer thickness. When the target value of the focus sensor is fixed, in particular, an actual pattern shape tends to differ from a desired pattern shape. Even if the above progressive focus exposure method is used under the same conditions (e.g., the relative moving range of the wafer surface with datum the imaging surface, so-called Z swing width, light amount, and the like), shape differences occur more or less. The above shape differences inevitably occur almost especially when patterns requiring predetermined shapes in the depth direction such as pixel patterns in a liquid crystal display device and contact hole patterns and other patterns requiring no predetermined shapes in the depth direction such as line-and-space patterns are to be formed on the same layer on the same substrate by exposure.
The present invention has been made in consideration of the above situation, and has as its first object to provide an exposure method and apparatus which can suppress variations in the shapes of pattern images transferred/formed on a substrate.
It is the second object of the present invention to provide an exposure method and apparatus which can transfer all patterns having different shapes onto the same substrate with high precision in desired shapes.
It is the third object of the present invention to provide a device manufacturing method which can improve the productivity of devices.
As described above, the photosensitive agent (resist) layer formed on the substrate varies in thickness from the central portion to peripheral portion of the substrate. Variations in the thickness of this resist layer at the respective positions on the substrate are determined by each resist coating unit. Therefore, the thickness distribution of a resist layer at the respective positions on a substrate can be obtained in advance by measuring the thickness of the resist layer. It is expected that the above variations in the shapes of pattern images due to variations in resist thickness can be suppressed to a certain degree by using this resist layer thickness distribution data. In consideration of this point, the present invention uses the following techniques and arrangements.
According to the first aspect of the present invention, there is provided a first exposure method of irradiating a mask on which a pattern is formed with an energy beam, and changing a positional relationship between an imaging plane of a projection optical system and a substrate in an optical axis direction of the projection optical system according to a predetermined procedure so that an irradiation area on a substrate surface irradiated with the energy beam through the projection optical system is always located in a range having a predetermined width in the optical axis direction and including the imaging plane, and a distribution of energy amounts supplied onto the substrate with respect to a position of the substrate surface with datum to the imaging plane becomes a desired distribution, thereby transferring the pattern onto the substrate, wherein the distribution of energy amounts in accordance with a position on the substrate of the area which is irradiated with the energy beam is changed in said lithography process upon transferring the pattern onto the substrate.
According to this method, when a pattern formed on a mask is to be projected onto a substrate and an image of the pattern is to be transferred/formed on the substrate by using the above progressive focus exposure method, the distribution of energy amounts supplied onto the substrate with respect to the position of the substrate surface with datum to the imaging plane is changed in accordance with the position of an irradiation area on the substrate which is irradiated with an energy beam through a projection optical system. With this operation, for example, in accordance with the information of the distribution of variations in resist layer thickness on the substrate, obtained in advance, the above distribution of energy amounts associated with the position of the substrate surface with datum to the imaging plane can be changed to reduce the influences of the distribution of variations in resist layer thickness. As a consequence, the depth of focus of the projection optical system can be substantially increased, and variations in the shapes of pattern images formed on the substrate at the respective positions can be suppressed.
In this case, the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system may be continuously changed. Alternatively, the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system may be intermittently changed.
In the first exposure method of the present invention, the distribution of energy amounts may be changed for each position of an area on the substrate which is irradiated with an energy beam through the projection optical system. However, if, for example, a plurality of divided areas are set on the substrate, the distribution of energy amounts may be changed in accordance with the position of a divided area subject to exposure on the substrate. In this case as well, the distribution of energy amounts may be changed for each position of an area on the substrate which is irradiated with an energy beam within one divided area.
In this specification, the expression xe2x80x9cchanging the distribution of energy amounts in accordance with a position of the area (to be also referred to as an irradiation area hereinafter) on the substrate which is irradiated with the energy beamxe2x80x9d indicates when a plurality of divided areas are set on the substrate, both that the distribution of energy amounts in each divided area (the distribution associated with each position on the substrate surface with datum to the imaging plane) is made uniform, and the distribution of energy amounts is changed in units of divided areas, and that the distribution of energy amounts is changed in accordance with the position of an irradiation area in each divided area (in this case, the distribution of energy amounts may be changed or not in units of divided areas).
In the first exposure method of the present invention, the distribution of energy amounts corresponding to a position on the substrate may be a distribution having peaks at a plurality of points including at least two points located near two end portions of the range having the predetermined width on the substrate surface with datum to the imaging plane while a predetermined integrated energy is supplied to each point on the substrate. In this case, the depth of focus of the projection optical system can be substantially increased. In addition, even in scanning exposure, the distribution curve of energy intensity at each point in an irradiation area can be made to have a sharp peak, and hence the resolution of a pattern image can be increased.
In the first exposure method of the present invention, various methods of changing the distribution of energy amounts are conceivable. For example, the speed or the like may be changed to change the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system. The distribution of energy amounts may be changed by changing the predetermined width.
In the first exposure method of the present invention, an integrated energy amount supplied to each point in an area irradiated with the energy beam may also be changed in accordance with a position on the substrate of the area. In this case, the influences of variations in the thickness of the resist layer formed on the substrate at the respective positions on the substrate can be reduced more effectively.
In this case, the integrated energy amount may be changed for each position of an irradiation area on the substrate which is irradiated with an energy beam. However, if, for example, a plurality of divided areas are set on the substrate, the distribution of energy amounts may be changed in accordance with the position of a divided area subject to exposure on the substrate. In this case as well, the distribution of energy amounts may be changed for each position of an irradiation area on the substrate within one divided area.
In this specification, the expression xe2x80x9cchanging an integrated energy amount supplied to each point in an area (irradiation area) irradiated with the energy beam in accordance with a position on the substrate of the areaxe2x80x9d indicates both that when a plurality of divided areas are set on the substrate, the integrated energy amount supplied to each point in each divided area is made uniform, and the integrated energy amount supplied to each point is changed in units of divided areas, and that the integrated energy amount supplied to each point is changed in accordance with the position of an irradiation area in each divided area (in this case, the integrated energy amount supplied to each point may be changed or not in units of divided areas).
According to the second aspect of the present invention, there is provided a second exposure method of irradiating a mask on which a pattern is formed with an energy beam, and changing a positional relationship between an imaging plane of a projection optical system and a substrate in an optical axis direction of the projection optical system according to a predetermined procedure so that an irradiation area on a substrate surface irradiated with the energy beam through the projection optical system is always located in a range having a predetermined width in the optical axis direction and including the imaging plane, and a distribution of energy amounts supplied onto the substrate with respect to a position of the substrate surface with datum to the imaging plane becomes a desired distribution, thereby transferring the pattern onto the substrate, wherein an integrated energy amount supplied to each point in an area irradiated with the energy beam is changed in accordance with a position on the substrate of the area upon transferring the pattern onto the substrate.
According to this method, when a pattern formed on a mask is to be projected onto a substrate and an image of the pattern is to be transferred/formed on the substrate by using the above progressive focus exposure method, the integrated energy amount supplied to each point in an area irradiated with an energy beam is changed in accordance with the position of an irradiation area on the substrate which is irradiated with an energy beam through a projection optical system. With this operation, for example, in accordance with the information of the distribution of variations in resist layer thickness on the substrate, obtained in advance, the integrated energy amount supplied to each point on the substrate can be changed to reduce the influences of the variations. As a consequence, the depth of focus of the projection optical system can be substantially increased by the progressive focus exposure method, and variations in the shapes of pattern images formed on the substrate at the respective positions can be suppressed by changing the integrated energy (exposure) amount in accordance with each position.
In this case, the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system may be continuously changed. Alternatively, the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system may be intermittently changed.
In the second exposure method of the present invention, the integrated energy amount may be changed for each position of an area on the substrate which is irradiated with an energy beam through the projection optical system. However, if a plurality of divided areas are set on the substrate, the integrated energy amount may be changed in accordance with a position on the substrate of a divided area subject to exposure. In this case as well, in accordance with the position of an area on the substrate which is irradiated with an energy beam, the integrated energy amount supplied into the area may be changed.
According to the third aspect of the present invention, there is provided a third exposure method of irradiating a mask on which a pattern is formed with an energy beam, and changing a positional relationship between an imaging plane of a projection optical system and a substrate in an optical axis direction of the projection optical system according to a predetermined procedure so that an irradiation area on a substrate surface irradiated with the energy beam through the projection optical system is always located in a range having a predetermined width in the optical axis direction and including the imaging plane, and a distribution of energy amounts supplied onto the substrate with respect to a position of the substrate surface with datum to the imaging plane becomes a desired distribution, thereby transferring the pattern onto the substrate, wherein a plurality of the patterns are prepared, and the distribution of energy amounts is changed in accordance with a pattern subject to transfer upon transferring each of the patterns onto the substrate.
According to this method, when a pattern is to be projected on a substrate by using the above progressive focus exposure method, and an image of the pattern is to be transferred/formed on the substrate, the distribution of energy amounts supplied onto the substrate with respect to the position of the substrate surface with datum to the imaging plane is changed in accordance with the pattern subject to transfer. For this reason, the above distribution of energy amounts with respect to the substrate surface with datum to the imaging plane can be changed to obtain a required depth of focus in accordance with, for example, the information of the state of the substrate surface based on the pattern shape or resist layer thickness. As a consequence, variations in the shapes of pattern images formed on the substrate at the respective positions can be suppressed. Even when, for example, a plurality of patterns having different shapes are to be formed on a substrate, all the patterns can be formed in desired shapes with high precision.
In this case, the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system may be continuously changed. Alternatively, the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system may be intermittently changed.
In the third exposure method of the present invention, an integrated energy amount supplied to each point in an area on the substrate which is irradiated with the energy beam can be changed in accordance with the pattern subject to the transfer.
In the third exposure method of the present invention, the plurality of patterns may be formed on the same mask or may be distributed on a plurality of different masks. In the latter case, a plurality of patterns may be respectively formed on different masks, or a plurality of (e.g., N) patterns may be dispersed on M ( less than N) different masks, which are smaller in number than the patterns.
According to the fourth aspect of the present invention, there is provided a fourth exposure method of irradiating a plurality of patterns with energy beams, and transferring the plurality of patterns onto a substrate by using a projection optical system, wherein at least one of a position of the substrate with respect to an imaging plane of the projection optical system in an optical axis direction of the projection optical system and a moving amount of the substrate in the optical axis direction of the projection optical system is set in accordance with the pattern subject to transfer upon transferring the pattern onto the substrate.
According to this method, when a pattern is to be transferred onto the substrate, at least one of the position of the substrate in the optical axis direction of the projection optical system with respect to the imaging plane of the projection optical system and the moving amount of the substrate in the optical axis direction of the projection optical system is set in accordance with the pattern subject to transfer. For this reason, when a plurality of pattern having different shapes in the depth direction are to be transferred onto a substrate, since exposure is performed after the position (focus position) of the substrate in the optical axis direction of the projection optical system or the depth of focus is set to an arbitrary value in accordance with each pattern, all the patterns transferred onto the substrate can be formed in desired shapes with high precision.
In this case, the setting can be performed in accordance with at least one of the position of the imaging plane of the projection optical system and the depth of focus.
In the fourth exposure method of the present invention, a plurality of patterns may be transferred on the different substrates and the plurality of patterns may also be transferred onto different areas on the same substrate.
In the fourth exposure method of the present invention, the plurality of patterns can be transferred onto adjacent areas on the substrate so as to join the patterns to each other.
In the fourth exposure method, an integrated energy amount to be supplied to each point in an area on the substrate which is irradiated with the energy beam may be independently set in accordance with the pattern subject to the transfer.
In the fourth exposure method of the present invention, the plurality of patterns may be dispersed on a plurality of masks, and the plurality of masks may be sequentially interchanged and the plurality of patterns may be transferred onto the substrate. In this case, a plurality of patterns may be respectively formed on different masks, or a plurality of (e.g., N) patterns may be distributed on M ( less than N) different masks, which are smaller in number than the patterns.
According to the fifth aspect of the present invention, there is provided a first exposure apparatus for transferring a pattern formed on a mask onto a substrate through a projection optical system, comprising an illumination system which illuminates the mask with an energy beam, a relative displacement unit which changes a positional relationship between a surface of the substrate and an imaging plane of the projection optical system on which a projected image of the pattern on the mask is formed in an optical axis direction of the projection optical system, and a control unit which changes a positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system via the relative displacement unit according to a predetermined procedure so that an irradiation area on the substrate surface which is irradiated with the energy beam through the projection optical system is always located in a range having a predetermined width in the optical axis direction and including the imaging plane of the projection optical system, and a distribution of energy amounts supplied onto the substrate with respect to a position of the substrate surface with datum to the imaging plane becomes a desired distribution, and changes the distribution of energy amounts in accordance with the position on the substrate of the area which is irradiated with the energy beam when the pattern is to be transferred onto the substrate when the pattern is to be transferred onto the substrate.
According to this apparatus, when a pattern formed on a mask is to be projected onto a substrate and an image of the pattern is to be transferred/formed on the substrate by using the above progressive focus exposure method, the control unit changes the distribution of energy amounts supplied onto the substrate with respect to the position of the substrate surface with datum to the imaging plane in accordance with the position of an irradiation area on the substrate which is irradiated with an energy beam through a projection optical system. With this operation, for example, in accordance with the information of the distribution of variations in resist layer thickness on the substrate, obtained in advance, the above distribution of energy amounts, supplied onto the substrate, associated with the position of the substrate surface with datum to the imaging plane can be changed to reduce the influences of the distribution of variations in resist layer thickness. As a consequence, the depth of focus of the projection optical system can be substantially increased, and variations in the shapes of pattern images formed on the substrate at the respective positions can be suppressed.
In this case, the control unit may continuously change the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system. Alternatively, the control unit may intermittently change the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system.
In the first exposure apparatus of the present invention, the control unit may also change an integrated energy amount supplied to each point in an area irradiated with the energy beam in accordance with a position on the substrate of the area. In this case, the influences of variations in the thickness of the resist layer formed on the substrate at the respective positions on the substrate can be reduced more effectively.
According to the sixth aspect of the present invention, there is provided a second exposure apparatus for transferring a pattern formed on a mask onto a substrate through a projection optical system, comprising an illumination system which illuminates the mask with an energy beam, a relative displacement unit which changes a positional relationship between a surface of the substrate and an imaging plane of the projection optical system on which a projected image of the pattern on the mask is formed in an optical axis direction of the projection optical system, and a control unit which changes a positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system via the relative displacement unit according to a predetermined procedure so that an irradiation area on the substrate surface which is irradiated with the energy beam through the projection optical system is always located in a range having a predetermined width in the optical axis direction and including the imaging plane of the projection optical system, and a distribution of energy amounts supplied onto the substrate with respect to a position of the substrate surface with datum to the imaging plane becomes a desired distribution, and changes an integrated energy amount supplied to each point in the area in accordance with the position on the substrate of the area which is irradiated with the energy beam when the pattern is to be transferred onto the substrate.
According to this apparatus, when a pattern formed on a mask is to be projected onto a substrate and an image of the pattern is to be transferred/formed on the substrate by using the above progressive focus exposure method, the control unit changes the integrated energy amount supplied to each point in an area irradiated with an energy beam in accordance with the position of an irradiation area on the substrate which is irradiated with an energy beam through a projection optical system. With this operation, for example, in accordance with the information of the distribution of variations in resist layer thickness on the substrate, obtained in advance, the integrated energy amount supplied to each point on the substrate can be changed to reduce the influences of the variations. As a consequence, the depth of focus of the projection optical system can be substantially increased by the progressive focus exposure method, and variations in the shapes of pattern images formed on the substrate at the respective positions can be suppressed by changing the integrated energy amount in accordance with each position.
In this case, the control unit may continuously change the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system. Alternatively, the control unit may intermittently change the positional relationship between the imaging plane and the substrate in the optical axis direction of the projection optical system.
According to the seventh aspect of the present invention, there is provided a third exposure apparatus for irradiating a plurality of patterns with energy beams and transferring the plurality of patterns onto a substrate by using a projection optical system, comprising an illumination system which illuminates the pattern with the energy beam, a control unit which sets at least one of a position of the substrate with respect to the imaging plane of the projection optical system in an optical axis direction of the projection optical system and a moving amount of the substrate in the optical axis direction of the projection optical system in accordance with the pattern subject to transfer when the pattern is to be transferred onto the substrate, and a relative displacement unit which changes a positional relationship between the substrate surface and the imaging plane of the projection optical system on which a projected image of the pattern is formed in the optical axis direction of the projection optical system in accordance with a setting made by the control unit.
According to this apparatus, when a pattern is to be transferred onto the substrate, the control unit sets at least one of the position of the substrate in the optical axis direction of the projection optical system with respect to the imaging plane of the projection optical system and the moving amount of the substrate in the optical axis direction of the projection optical system in accordance with the pattern subject to transfer. The relative displacement unit changes the positional relationship between the substrate and the imaging plane of the projection optical system on which the projected image of the pattern is formed in the optical axis direction of the projection optical system in accordance with the setting made by the control unit. For this reason, when a plurality of patterns having different shapes in the depth direction are to be transferred onto a substrate, since exposure is performed while the position (focus position) of the substrate in the optical axis direction of the projection optical system or the depth of focus is set to a value corresponding to each pattern, all the patterns transferred onto the substrate can be formed in desired shapes with high precision.
In the lithography process, by performing exposure using one of the first to fourth exposure methods of the present invention, variations in the shapes of pattern images formed on a substrate can be suppressed. As a consequence, the yield of devices as final products improves, and the productivity can be improved. Likewise, in the lithography process, by performing exposure using one of the first to third exposure apparatuses of the present invention, variations in the shapes of pattern images formed on the substrate can be suppressed. As a consequence, the yield of devices as final products improves, and the productivity can be improved. According to still another aspect of the present invention, there is provided a device manufacturing method using one of the first to fourth exposure methods of the present invention or one of the first to third exposure apparatuses of the present invention.